Breast cancer will claim the lives of approximately 39,000 American women this year alone. Uncovering novel molecular mechanisms of breast cancer pathogenesis is therefore critical to fill gaps in our understanding of this disease and to save the lives of thousands of women every year. Altered gene expression is one critical point of dysregulation in cancer and there is increasing evidence that post-transcriptional processing of mRNA transcripts plays a major role in ensuring proper gene expression. Post-transcriptional events are mediated by a myriad of RNA-binding proteins (RBPs), one key class of which is comprised of poly (A) binding proteins (Pabs). A novel CCCH zinc finger Pab, ZC3H14, has recently been linked to the Estrogen Receptor (ER) status of breast tumors. Although the molecular function of ZC3H14 is unknown, the budding yeast counterpart, Nab2, is required for proper control of poly (A) tail length and mRNA export from the nucleus, consistent with a critical role for ZC3H14 in post-transcriptional regulation. Although ZC3H14 is a Pab, our preliminary data suggest that specific mRNA transcripts are modulated by ZC3H14 in breast cancer cells. ZC3H14 may achieve this transcript specificity via another RBP that recognizes specific mRNAs, such as Human Antigen R (HuR), an AU-rich element binding protein already strongly linked to breast cancer. A previous study in yeast demonstrated an interaction between Nab2 and Pub1 (S. cerevisiae HuR ortholog) that influenced the stability of target mRNA transcripts. In a genome-wide analysis of ZC3H14 and HuR, we identified evidence of consensus cis-elements located within the 3' UTR of candidate mRNA targets of the two proteins as well as a significant overlap between candidate targets. These data suggest that ZC3H14, like HuR, has specific mRNA targets, and that ZC3H14 and HuR may have a functional relationship. In this proposal we will employ multiple approaches to test our hypothesis that ZC3H14 binds to specific cis- elements within the 3' UTR of target mRNA transcripts to modulate their stability and/or poly (A) tail length, potentially in concert with HuR. In the long-term, we seek to provide further insight into the role that RBPs play in modulating gene expression. In our first aim, we will validate specific ZC3H14 targets and identify candidate ZC3H14 regulatory sequences in these target mRNAs to assess the post-transcriptional consequence of ZC3H14 binding to target mRNAs. In our second aim, we will examine the functional relationship between ZC3H14 and HuR in modulating target mRNAs. This study will provide insight into the role of poly (A) RBPs such as ZC3H14 as post-transcriptional regulatory players and their potential involvement in breast cancer.